This invention relates in general to vehicle electronically controlled chassis systems. More particularly the invention relates to chassis systems having anti-lock brakes, traction control, rear wheel steer, etc., and uses tire force characteristics in that system to enhance the overall performance. Many vehicles today come equipped with advanced chassis systems such as anti-lock brake systems, traction control, vehicle stability control and other electronically operated systems that enhance vehicle performance as a function of road conditions. As a part of many of these advanced chassis systems, tire sensors are incorporated on the vehicle tires to obtain information about the interaction between the tires and the road surface that is in turn processed by a controller to regulate the tire forces by selectively maintaining, increasing, or decreasing brake or drive torque and/or slip angle at the associated tire. It is known to use wheel rotational speed or force sensors to obtain the data necessary for the operation of the control system.
For example in U.S. Pat. No. 6,330,496 to Latarnik et al., a method of adjusting the driving performance of a vehicle based on data obtained from tire sensors is disclosed. Particularly, Latarnik et al. discloses using nominal forces acting on the tires as the control quantity which is used by a controller to regulate the brake pressure or engine drive torque. The nominal forces can be converted into brake pressure variations, absolute brake pressures, valve actuation periods or current intensities, or can be used to vary the engine drive torque to control the driven tires. However, the forces sensed on the tires in the Latarnik et al. method are actual forces and torques, and are taken in longitudinal, transverse and vertical directions. Additional inputs for determining nominal quantities can be individual wheel rotational speeds or a vehicle reference speed, for example.
U.S. Pat. No. 5,247,831 to Fioravanti also discloses a method for optimizing the behavior of a vehicle based on estimating the tire footprint. Specifically, the signals monitored to establish footprint behavior are the dynamics of the center of gravity of the vehicle, rotation of the wheels in the vertical plane (driving and braking forces), rotation of the wheels in the horizontal place (steering angle), and vertical movement of the wheels. A processor calculates the footprint of each wheel and processes the data based on control parameters to control various transmission, braking, steering, and suspension members of the vehicle to optimize the performance and safety capabilities of the vehicle. This process can be done continuously to check the driving conditions and optimize the operations of a vehicle.
Additionally, it is known how to detect whether a vehicle has one or more tires having low air pressure or a flat. This information can be transmitted to the driver so that the driver can take remedial measures. For example, in U.S. Pat. No. 5,721,374 to Siekinen et al., detecting low tire pressure is accomplished by comparing wheel speeds using sensors in place on the wheels or within the braking system. U.S. Pat. No. 5,591,906 to Okawa et al. discloses a tire pressure drop detecting device to be used in conjunction with a run-flat tire. Generally, a run-flat tire is designed to operate under a “flat-tire” event, albeit at reduced speeds and for a limited distance. Under such operation, Okawa contemplates a mechanism to detect such a pressure drop and notify the driver, so that the speed and distance limitations of the run-flat tire are not exceeded and safety is enhanced.
While the above-described systems and other existing systems have effectively managed the operation of vehicle control systems, there is a need for greater overall control of a vehicle using tire sensors to detect tire conditions and operate a control system based on the sensed data.